Laminated glass is widely utilized in industry, most notably for motor vehicle windshields and other safety glass. Generally, laminated glass comprises two sheet-like substrates (e.g., glass sheets) and an interlayer (e.g., a tear-resistant plastic) positioned between the two substrates. An advantage of using laminated glass is that, when impacted by an object, the laminated glass retains its overall structural integrity and reduces the occurrence of flying glass resulting from glass breakage. Using laminated glass for motor vehicle windows, for example, helps ensure the safety of drivers and passengers in the event of accidents. Similarly, using laminated glass in other safety glass applications (hurricane glass, blast-resistant glass, etc.) helps ensure the safety of bystanders.
Generally, the manufacture of laminated glass is known to involve two operations: (1) an assembly operation, and (2) an autoclave operation. In the assembly operation, the interlayer is positioned between two glass substrates to form a sandwich, which is then heated (commonly to a temperature of between about 120° F. and about 170° F.) and roller pressed to initiate removal of air trapped between the interlayer and to initiate adhesion of the interlayer to the glass. In the autoclave operation, the sandwich is exposed to an elevated temperature (commonly between about 275° F. and about 300° F.) and an elevated atmospheric pressure (commonly between about 150 psig and about 190 psig) until there is complete adhesion of the interlayer to the glass and complete dissolution of air trapped within the interlayer. It is not uncommon for the autoclave operation to last two hours or four hours per treatment.
One of the major drawbacks of manufacturing laminated glass with an autoclave method is the long autoclave operation time. Conventional autoclave methods are batch processes. As a result, they are limited in terms of throughput by the batch processing requirements of the autoclave. As noted above, it commonly takes about two or four hours, depending on batch size, for a batch of laminates to be autoclaved. It would be desirable to provide a continuous (i.e., non-batch) method for producing laminated glass.
A related drawback of producing autoclaved laminated glass is that defects in the laminated glass sometimes do not appear until after the laminated glass has been autoclaved. For example, manufacturers commonly have to wait about two hours, and sometimes about four hours, for each batch of autoclaved laminated glass before detecting any unexpected defects that may appear. Thus, it would be desirable to provide a continuous non-autoclave process.
Non-autoclave laminated glass is disclosed in U.S. Pat. No. 5,536,347 (Moran), and U.S. Pat. No. 3,234,062 (Morris), the entire teachings of each of which are incorporated herein by reference. While these references disclose non-autoclave laminated glass, both have significant limitations. For example, both references disclose vacuum processes wherein complicated vacuum bags, vacuum rings, or the like are used. It would be desirable to provide a non-autoclave laminated glass method that can be preferred under ambient atmospheric conditions and that does not require vacuum bags, vacuum rings, or any other complicated devices.